The present invention relates to an infrared type gas analyzer, in particular an infrared type gas analyzer with a correlation filter for continuously measuring a concentration of a specific component in a gas or vapor by utilizing an infrared absorption effect which is an inherent characteristic of gas molecules.
FIG. 4 is a block diagram for showing a CO analyzer which is an example of an infrared type gas analyzer provided with a conventional correlation filter. In the infrared type gas analyzer, infrared light from a light source 11 is irradiated to a measuring cell 13 through a gas correlation filter 120 The measuring cell 13 includes an introduction port 13a and a discharge port 13b so that a sample gas can continuously flow. An optical filter 13c disposed on a front face of the measuring cell 13 permits only the infrared light in a CO absorption wavelength range to pass therethrough, so that an interference error by a gas component close to the CO absorption wavelength range, such as CO.sub.2, can be removed.
As shown in FIG. 5, the gas correlation filter 12 includes a CO cell 12a containing a CO gas to be measured, and an N.sub.2 cell 12b containing an N.sub.2 gas, so called zero gas, not absorbing the infrared light, and is appropriately driven by a motor 14 shown in FIG. 4.
A sensor 15 alternately detects the infrared light obtained through the CO cell 12a and the infrared light obtained through the N.sub.2 cell 12b, and a data processing section 16 calculates a CO concentration in the sample gas from the alternately detected data.
More specifically, since the infrared light in the CO absorption wavelength range is completely absorbed from the infrared light passing through the CO cell 12a, a component in the CO absorption wavelength range of the infrared light in the data detected by the sensor 15 becomes zero regardless of a CO concentration in the measuring cell 13. On the other hand, data detected by the sensor 15 of the infrared light transmitted through the N.sub.2 cell 12b becomes a value corresponding to the CO concentration in the measuring cell 13 since the component in the CO absorption wavelength range remains as it is. Therefore, the CO concentration in the sample gas can be obtained by calculating a ratio of both the values at the data processing section 16.
In the infrared type gas analyzer as described above, a zero value and a measuring range, i e. span, are required to be periodically corrected by using a standard for comparisons Heretofore, a zero-point or span-point has been corrected or calibrated by flowing a zero gas or span gas instead of a gas to be measured during the measurement by using electromagnetic valves or the like. Therefore, since the correction gas is released to the atmosphere in succession, consumption of the correction gas is extremely increased in comparison with other gas analyzers to thereby raise a correction cost.
Therefore, it has been practiced that at a time of a span correction, a correction gas is not used, and instead, an amount of the infrared light is adjusted by providing a light regulating plate or douser in a light path of the infrared ray to coincide with an amount of the infrared light reaching the sensor without being absorbed by a gas having a known concentration when the gas is caused to flow. More specifically, in case a zero correction of the gas analyzer is carried out, a zero gas is applied to flow through the measuring cell to perform the zero correction. Then, in case a span correction is carried out, the zero gas is applied to flow through the measuring cell, as in the zero correction, and the span correction is carried out in a state where the light regulating plate is inserted into the infrared light path to precisely coincide therewith. Incidentally, it is necessary that an output value of the light regulating plate is beforehand confirmed by the span gas, because the output value at this time becomes a correction value.
Also, an optical filter or a filter containing a gas therein may be used instead of the light regulating plate.
In the conventional infrared type gas analyzer, the zero and span corrections are carried out as described hereinabove. However, there have been defects such that mechanisms for moving the light regulating plate and optical filter are required to thereby complicate a structure of the infrared type gas analyzer. Also, when the light regulating plate or optical filter is repeatedly moved, it must be placed at a position precisely coinciding with the infrared light path. Thus, a position detector is also required to thereby complicate the structure.
In view of the foregoing, the present invention has been made, and an object of the present invention is to provide an infrared type gas analyzer having a simple structure by which a correction or calibration can be simply carried out without complicated operations.
Further objects and advantages of the invention will be apparent from the following description of the invention